r. i. t multidisciplinary senior design phase-appropriate feasibility analysis rochester institute...
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R . I . TMultidisciplinary Senior
Design
Phase-AppropriateFeasibility Analysis
Rochester Institute of TechnologyMechanical Engineering Department
Rochester, NY USA
R . I . TMultidisciplinary Senior
Design
Session Objectives
• Motivation: Risk Analysis, Metrics & Specs• Assignment• Examples
• EE• CE• ISE/ID• ME
R . I . TMultidisciplinary Senior
Design
Engineering Requirement
• Requirement = Metric + Specification• Metrics = what measurement you are going to
make to determine whether your design is successful
• Specification = the target (or minimally acceptable or ideal) value to achieve for that measurement
Use preliminary feasibility here!
R . I . TMultidisciplinary Senior
Design
Project Risks
• Schedule risks• Things take longer than expected to design, order,
receive, build, test
• Personnel risks• Staffing is insufficient, team member is unable to
complete his or her work, team dynamics become an issue
• Resource risks• Project is over budget, lack space, equipment missing,
can’t get into machine shop, etc.
Use preliminary feasibility here!
R . I . TMultidisciplinary Senior
Design
Technical Risks
• Risks associated with your design.• Design is not feasible• Specs are not feasible• Components don’t perform to spec• Components can’t be manufactured as designed• Technology is not as developed as anticipated• Expertise of team is overestimated
Use preliminary feasibility here!
R . I . TMultidisciplinary Senior
Design
Session Objectives
• Motivation: Risk Analysis, Metrics & Specs• Assignment• Examples
• EE• CE• ISE/ID• ME
R . I . TMultidisciplinary Senior
Design
Prepare for class:
• List one question about your design that can be answered by phase-appropriate feasibility analysis• Discuss this as a team ahead of time – do not duplicate effort
between team members!
• Determine whether the question is best answered with analysis, benchmarking, or prototyping
• List assumptions, governing equations, materials, competitors, etc. as appropriate
• Use simple tools to solve the problem in your logbook.
• You will present this to your peers during the next class!
R . I . TMultidisciplinary Senior
Design
Session Objectives
• Motivation: Risk Analysis, Metrics & Specs• Assignment• Examples
• Disclaimer: taken mostly as-is from team documents!• EE• CE• ISE/ID• ME
R . I . TMultidisciplinary Senior
Design
EE Example from MSD - Analysis
• From P12015/6 Navigation Aid for Blind Person
• Preliminary feasibility question #1: how much power will
our device consumer?
• Assumptions: • Use some good candidate off-the-shelf components and an off-
the-shelf battery.
• It takes 20 minutes at most for the user to move from one
location to another, and this happens at most 10 times per day.
R . I . TMultidisciplinary Senior
Design
P12015: Power Calculations
RFID Reader 1.5796 W*hr
Motors 0.021166667 W*hr
MCU 0.047784 W*hr
Magnetometer 0.0913 W*hr
Keypad 0.083333333 W*hr
*Sum 1.823184 W*hr
*For (10) 20 minute intervals of navigation
R . I . TMultidisciplinary Senior
Design
Hold on a minute! Significant figures…
• 0.021166667?????• Use datasheets and maintain significant figures
• That give us…
R . I . TMultidisciplinary Senior
Design
P12015: Better Power Calculations
RFID Reader 1.58 W*hr
Motors 0.02 W*hr
MCU 0.047 W*hr
Magnetometer 0.09 W*hr
Keypad 0.08 W*hr
*Sum 1.817 W*hr
Math skills involved: Reading datasheets, multiplying voltage and current, maintaining significant figures.
Value to team: High!
*For (10) 20 minute intervals of navigation
R . I . TMultidisciplinary Senior
Design
ME/EE Example from MSD – Analysis & Benchmarking
• From P13002 Active Ankle Foot Orthotic• Preliminary feasibility question: How fast of a
walking speed can our sensor reliably measure?
• Assumptions:• Gait data follows a 4th order Fourier series (i.e., signal
content 4x fundamental gait frequency)• Using IR sensors to quantify gait patterns
R . I . TMultidisciplinary Senior
Design
Benchmarking: representative IR sensor
Don’t use first 53 ms of data!
Could take as long as 48 ms to acquire each additional sample.
R . I . TMultidisciplinary Senior
Design
Analysis
• 48 ms per sample ~20 samples/sec
• Looking for frequency content 4x fundamental gait frequency, Nyquist criterion says to sample at 2x that take 8 samples per step
• Max quantifiable gait speed is:
• (20 samples/sec) / (8 samples/step) = 2.25 steps/sec
• Use this information to bound system specs!
R . I . TMultidisciplinary Senior
Design
CE Example from MSD – Analysis & Benchmarking
• From P12015/6 Navigation Aid for Blind Person
• Preliminary feasibility question #2: How much onboard
storage do we need for a building map?
• Assumptions: • Building map will be stored onboard and will be the biggest
memory hog.
R . I . TMultidisciplinary Senior
Design
Map representation
• Major considerations include the size of the map file (limited memory
space on the board), the ASCII character set requirement spec, and
the 1000 maximum tags spec• Maps consist of:
o tags, each with an ID (12 bytes) and X and Y coordinates in inches
or centimeters (range: 0~4000);o map vertices (e.g., rooms, water fountains, bathrooms, hall
intersections), each with X and Y coordinates;o walking paths between vertices, which include the start and end
verticeso assumption that the device is currently only being used to navigate
one floor of one building
R . I . TMultidisciplinary Senior
Design
Map representation (continued)
• Possible solution: use base64 notation (ASCII-safe but still small)o Tags, with their large ID fields, will likely comprise the largest part of
the fileo With base64 notation, tag IDs require 16 'digits' and the coordinates
will use 2+2 'digits' = total of 20 bytes per tago The MCU memory must be able to accommodate up to 1000 tags =
20KB minimum per map (restricts MCU choice!)• Store the graph underlying the map of destinations and paths densely
(low connectedness)
R . I . TMultidisciplinary Senior
Design
ISE & ID Example from MSD - Prototyping
• P14042 – Una-Crutch
• Preliminary Feasibility Question: What type of design is
going to be most appealing to users? Can we find out
before spending lots of time doing detailed analysis and
manufacturing planning?
• Approach: foam + PVC pipe models (non-load bearing)
and user survey
R . I . TMultidisciplinary Senior
Design
Axilla Pads and HandlesPrototypes Created
R . I . TMultidisciplinary Senior
Design
C
B
Frames and Connective MechanismsPrototypes B, C, and G
G
R . I . TMultidisciplinary Senior
Design
ME Example from MSD - Analysis
• P12007 – Equilibrate Balance Assessment System
• Preliminary Feasibility Question: Can we reduce system
weight without compromising stability/deflection?
• Approach: ANSYS Before using finite element software,
conduct parametric analysis using Strength of Materials
models (save ANSYS for detailed design phase)
R . I . TMultidisciplinary Senior
Design
Full system: team targets footplates for weight reduction
System weight: 44 lb
Footplates: 8.7 lb!
Customer: “Reduce weight, reduce cost, increase functionality”
R . I . TMultidisciplinary Senior
Design
Systems-Level Design
Simple spreadsheet analysis of representative loading scenario allows the team to evaluate different materials and thicknesses.
Generous on assumptions, but lets us compare options in an educated manner. Once a decision is made, detailed design can focus on a single material configuration
R . I . TMultidisciplinary Senior
Design
Summary
• Decide what questions you need to answer
• Decide the best means of answering them (analysis,
benchmarking, prototyping)
• Use phase-specific tools• Hand calculations
• Logic
• Benchmarking
• Basic physics
• Simple prototypes